The present invention relates to a starting device for an internal combustion engine, in particular a pull-rope type starting device for at least one two-stroke or four-stroke motor.
In the past, the operation of a starting device for an internal combustion engine, in particular of a pull-rope type starting device for a two-stroke or four-stroke motor, has often caused problems because during the starting process the compression in the internal combustion engine periodically leads to high reaction forces occurring as a result of which changing and temporarily very considerable forces act on the hand of the operator.
The load peaks which occur at the handle, in particular at the starter handle or pull handle of the starting device, are accordingly larger, the lighter the rotating mass of the internal combustion engine. In concrete terms this means that the torque to be produced at the motor shaft is subject to considerable fluctuations, because in the compression phase of the piston, up to the dead centre, a very considerable torque is to be produced, while in the expansion phase, the torque to be produced drops considerably, at times even dropping to zero.
In order to reduce transfer of these particularly strong reaction forces, which are caused as a result of the compression in the internal combustion engine, on the handle of the starting device, thus facilitating the starting process, printed publication DE-P 41 35 405 A1, which discloses a starting device of the type mentioned in the introduction, proposes that the fluctuations in the torque which has to be produced at the motor shaft be elastically cushioned.
To this effect, an elastic element is coupled between the pulley or rope drum associated with the load transfer means of the handle, in particular the starter rope or pull rope, and the engaging element, in particular the ratchet-type engaging element, of the crankshaft. By means of said elastic member, the pull movement during the starting process, which pull movement is transferred by the handle and the load transfer means, is somewhat freed of the above-mentioned fluctuations, or, in an ideal case, is completely freed. (An earlier attempt to design the load transfer means so as to be elastic itself led to unsatisfactory results.)
Probably the earliest proposal concerning an in-line arrangement of such an elastic coupling element is contained in the Japanese printed specification for a utility model Y-H616964 (Starting Industrial Co., Ltd.). The European patent application EP 1 203 883 A2 contains a newer proposal submitted by the same applicant.
Furthermore, a proposal was recently developed in which, during starting, the elastic coupling element, which is designed as a spiral spring, is rotated by an angle of rotation of approximately 270 degrees to approximately 280 degrees, which provides good starting characteristics. When this maximum angle of rotation has been reached, the spiral spring places itself against the shaft, due to becoming smaller as a result of rotation. This placement of the spiral spring against the shaft results in a blockage of any further rotation so that the engaging element of the crankshaft is forced to rotate with the pulley or rope drum.
However, in practical application, this design (such as the light-start system supplied by Starting Industrial Co., Ltd., according to the so-called coil-spring principle) has been associated with disadvantages in that there is a design-related gap between the pulley or rope drum and the engaging element, with said design-related gap being defined by the longitudinal tolerance of three components, and with said design-related gap being difficult to achieve in the required quality in series production.
Consequently, due to the operating principle of the spiral spring which—blocking any further rotary movement beyond approximately 270 degrees to approximately 280 degrees—places itself around the bearing axles, a coil of this spiral spring is pushed on one side into the gap or interspace between the pulley or rope drum and the (ratchet-type) engaging element, because the spiral spring has to absorb the entire force of the load transfer means, i.e. the entire force of the pull rope.
This is illustrated in FIG. 1, wherein a rope drum 4 is rotatably held in a housing 1. When the rope drum 4 is made to rotate by the starter rope or pull rope 9 being pulled, such as by means of a starter handle (not shown in FIG. 1) to generate the drive torque for a motor shaft. When this occurs, the elastic coupling element, in the form of a spiral spring 6, compresses around an axle of the rope drum 4 and an axle of the engaging element 5. However, due to a gap 18 between these axles, the coil spring 6 is pushed into the gap or interspace between the rope drum and the engaging element, such as is illustrated in FIG. 1. It will be appreciated by those skilled in the art that the spring 6 illustrated in FIG. 1 is only partially impinging upon the gap 18, and that, in fact, a portion of the spring 6 can become completely lodged within the gap 18 between the rope drum 4 and the engaging element 5.
In conclusion, this means that when a specific tolerance dimension is exceeded, at least part of a coil of the spiral spring 6 enters the gap 18 between the pulley or rope drum 4 and the engaging elements 5 which are connected by the spiral spring 6, thus naturally becoming overstretched and sustaining permanent deformation. As a result of this, the system ceases to function properly and blocks.
Furthermore, it must be considered that during each starting process the elastic coupling element, which is a spiral spring, comes to rest on the shaft (angular limitation of the system to approximately 270 degrees to approximately 280 degrees), and that the forces of the pull rope which are required for overcoming the compression force are only transmitted by way of the spiral spring. In extreme cases this can result in the spiral spring breaking so that the starting device ceases to function and the internal combustion engine can no longer be started at all.
It is also possible for fragments of the broken spiral spring to damage adjacent components of the starting device.
Accordingly, there is a continuing need for a pull-rope starting device for an internal combustion engine which prevents the elastic coupling element (coil spring) from entering the gap between the rope drum and engaging element. The present invention fulfills this need, and provides other related advantages.